Shuttle speed control device

ABSTRACT

Disclosed for a sound motion picture camera is an improved shuttle speed  trol device including a film loop sensor sensitive to slight variations in the film loop for causing the speed of the shuttle to be changed by a simple brake device utilizing powers of the drive motor whereby less force is required for sensing the size of the film loop to maintain picture-sound synchronization.

This invention relates to a shuttle speed control device for either amotion picture camera or a motion picture projector for handling motionpicture film on which sound is to be recorded simultaneously as theimage is photographed, and from which sound is to be reproducedsimultaneously.

In a simultaneous recording sound motion picture camera, film istransported intermittently past an exposure station, and is transportedcontinuously past a sound station. The sound for a particular film frameimage is displaced along the film by a short distance, e.g., 18 frames.Thus, for "lip synchronized" recording and playback, the sound to framespacing must be maintained constant.

In many sound motion picture cameras, two motors are used respectivelyto drive a shuttle to intermittently move film past an aperture at theexposure station, and to drive a capstan to continuously move film at aconstant rate past a transducer at the sound station. Although themotors may be manufactured uniformly, differences occur in the rate atwhich film is transported through the stations. Such differencesaccumulate during transporting a length of film resulting in slightchanges in the film length between the stations. The between stationfilm length increases or decreases so that spacing becomes either 19 or20 frames, or 17 frames causing loss of picture-sound-synchronizationafter a few inches of film is transported. If the error is permitted toaccumulate over a length of film, the lack ofpicture-sound-synchronization, would be obviously noticeable and filmdamage could occur.

Other sound motion picture cameras use only one motor to drive both theshuttle and the capstan. Nevertheless, the film is sometimes transportedthrough the exposure and sound stations at different rates because ofsmall errors in the transmission mechanisms. That is, as the film ispulled out of the film supply cartridge, the film is sometimestransported through the exposure station slower than the rate it ismoved through the sound station. Alternatively, the film is sometimesmoved faster by the shuttle at the exposure station than by the capstanat the sound station.

Between the exposure station and the sound station, the film path isprovided with a loop which becomes larger or smaller depending on therelative speeds of the shuttle and the capstan. When the loop becomessmaller, the film may be stretched and may be caused to slip in thesound station as the friction of the capstan against the film is weakerthan the more positive force applied by the shuttle. Hence, the soundwould be caused to be distorted when slippage occurs whereby the film isnot uniformly pressed against the transducer at the sound station.Further, when the loop becomes larger, the film can be stopped in thecamera due to jamming or the like. In either case, the changes in filmlength between the stations can cause aberrations in the sound as wellas loss of synchronization between the sound and the picture.

To overcome the problems set forth above and to maintain the picture andsound in "lip synchronization", an improved shuttle speed control deviceis provided. A film loop sensor located between the capstan and theshuttle in a motion picture camera is well known. When such sensors areof the electric type and respond sensitively to changes in the size ofthe film loop, the shuttle can become unstable in the rates at which itis transporting film. Generally, an individual motor is required todrive the shuttle and another motor is required to drive the capstan asthe shuttle speed is continuously varied while the capstan is driven ata constant speed.

Another well known device often used in varying output speed is atapered pulley which is installed on the motor shaft for output to theshuttle. Movably positioned on the pulley is a belt which movedrespectively further in or further out on the pulley to change the speedof the shuttle in response to the movement. However, a large force isrequired to move the belt on the pulley which force cannot be readilyobtained by having the sensor engage the film directly and to directlymove the belt, thereby reducing sensitivity of the sensor.

This invention is an improved shuttle speed control device which removesthe above mentioned shortcomings. The sensor is arranged to be sensitiveto the slight variations of the film loop causing the speed of theshuttle to be changed accurately and sensitively. This action isaccomplished with a simple mechanism whereby the sensor actuates a brakeand causes the position of the belt to be changed by utilizing the forceof the motor. Hence, the sensor is actuated to respond with significantsensitivity to changes in the size of the film loop.

An object of the present invention is to provide an improved shuttlespeed control device for a sound motion picture instrument in whichsound-picture synchronization is maintained by a power drive whichenhances sensitivity of the film loop sensor.

Other objects and advantages of the invention will become apparent fromthe detailed description which follows when taken in conjunction withthe accompanying drawings in which like numerals refer to like parts.

IN THE DRAWINGS

FIG. 1 is a schematic representation of the speed changing device withthe brake actuated;

FIG. 2 is a similar schematic representation of the speed changingdevice with the brake released; and

FIG. 3 is an elevational view of a camera with the speed changingdevice, according to this invention, arranged in operative orientation.

Referring now to the FIGS. 1 and 2, a speed changing device is shownconnected to a motor 1 having a shaft 2 driven thereby. The deviceincludes a half pulley 3 which is tapered on one side and is fixed tothe shaft 2 for rotation therewith. A half pulley 4 is arranged on theshaft 2 opposite the half pulley 3. The half pulley 4 is slidableaxially of the shaft 2 relative to the fixed half pulley 3. The halfpulley -cone portion 3 and the half pulley -cone portion 4 are rotatedtogether by a pin 5 which extends from half pulley 3 into a hole 6 inhalf pulley 4.

In addition to the pin receiving hole 6 formed in one face of halfpulley 4, the other face of that half pulley is provided with a slantedpawl 7. Cooperating with the claw 7 is another slanted pawl 8 on a brakedisk 9 rotatable on shaft 2 but fixed against axial movement on theshaft by a fixed ring member 10. The slanted pawls 7 and 8 have facinginclined cam surfaces which rise to a height equal to the maximumspacing between the half pulleys.

Adjacent the peripheral surface of the brake disc 9 is arranged a brakemember 11, which is carried by an end of a film loop sensor 12. A spring13 continuously biases the brake member of the loop sensor 12 towardengagement with the brake disc 9 to control rotation of the brake diskand therefore the rate of rotation of a transmission member shown asbelt 14 which passes between the half pulleys 3 and 4.

When the shaft 2 of the motor 1 is rotated in the direction A2, shown inFIG. 1 as being clockwise, half pulley 3 is rotated in the samedirection. By the pin 5 and hole connection of half pulley 3 with halfpulley 4, the latter pulley is rotated at the same rate as the pulleyfixed to shaft 2. Similarly, brake disk 9 is rotated at the same ratesince it is driven by the pawl 8 through the connection to the motorshaft 2 by the half pulley portions. However, when the brake disc 9 isengaged by brake 11, the disc is slowed slightly and the slanted face ofthe pawl 8 causes the half pulley 4 to be raised toward the half pulley3 in the direction of arrow A4. Therefore, the belt 14 rides at maximumheight on the pulley periphery formed by the half pulley portions 3 and4.

The speed of belt 14 becomes slower than as shown in FIG. 1 when thebrake 11 is removed from the brake disc 9 as shown in FIG. 2. That is,when the brake disc 9 is free of the restraint by brake 11, the brakedisc rotates faster. As the disc rotates, pawl 8 of the disc meshes withthe pawl 7 of the half pulley 4 and therefore permits the half pulley 4to move in the direction of arrow A4¹. As the space between the halfpulley 3 and half pulley 4 with the pawl becomes wider, the belt 14sinks between the half pulley members thereby slowing the rate ofrotation of the belt.

In FIG. 3, the shuttle control device is shown arranged to cooperatewith pertinent components of a sound motion picture camera of the typein which sound is recorded directly on a film. In this preferredembodiment, the rate of film transport is 18 frames per second. In thecamera, a driving shaft or transmission 15 is driven by the belt 14 todrive a shuttle 16 for intermittently transporting a film 17 through theexposure station. The sound station of the camera includes a recordinghead or transducer 18 across which film is transported by a capstan 19and a pinch or pressure roller 20. The capstan is powered either by themotor 1 or a second separate motor 1'. Together, the capstan and thepinch roller constantly transport the film through the sound station atexactly 18 frames per second.

The output shaft 2 of the motor 1 is coupled to the capstan 19 and bythe shuttle speed control device to a pulley 21 from which the shuttle16 is connected. The shuttle speed control device is actuated responsiveto the sensor 12, pivoted about an axis 22 with one end engaging a loop23, formed in the film 17 between the exposure and sound station. Theother end of the sensor carries the brake pad 11. If the film istransported at the same rate by both the shuttle 16 and the capstan 19,the loop size is constant and the image and sound are synchronized.However, when the speeds at which film 17 is transported by the shuttleand the capstan differ, although slightly, the loop is enlarged orreduced in response thereto. The differential in loop size, occurs dueto the slip in the transporting mechanism, the frictional resistance offilm, and errors accumulating in the film transporting between twotransporting portions. When the loop size increases, the sensor ispivoted about axis 22 to remove the brake 11 from the braking disk 9 asshown in FIG. 2. Thereby, the belt 14 is permitted to move to a smallerdiameter on half pulley 3 and half pulley 4 as the pulley portionsseparate. Thus, the rate of operation of the shuttle 16 is slowedcausing the capstan to transport film faster, wherein the excess filmlength generating the film loop 23 is reduced.

Alternatively, when the shuttle 16 transports film too slowly the filmloop is reduced from a preferred size. Since the sensor 12 is biasedagainst the film by spring 13, the brake 11 is moved into engagementwith the brake disk 9. As above described, the restraint on the brakedisk causes the belt 14 to be run on the outer periphery or largerdiameter of the half pulley portions 3 and 4 so as to drive the shuttle16 at a faster rate. The increase in shuttle rate continues until filmis accumulated in the film loop thereby releasing the brake from thebrake disc.

During camera operation, the length of film between the shuttle 16 andthe transducer 18 is maintained constant, at for example 18 frames byrepeating rapidly the abovementioned two actions of increasing anddecreasing the film loop size as required.

In summary, a highly sensitive shuttle speed control device is describedwhereby the shuttle speed is adjusted periodically and smoothly. Thesmoothness of this action is enhanced by the separation of the force todrive the shuttle and the force to detect the film loop size.

What I claim is:
 1. A shuttle speed control device for .[.a.]. soundmotion picture .[.camera.]. .Iadd.cameras and projectors.Iaddend.including a drive motor having an output shaft driving ashuttle for transporting film intermittently through an exposure stationand a capstan for transporting film constantly through a sound station,and a film loop sensor arranged between the exposure station and thesound station, the control device comprising:a first half pulley fixedto said motor output shaft; a second half pulley coupled to said firsthalf pulley and adjustable along said motor output shaft; transmissionmeans arranged about said half pulleys and coupled to said shuttle forpowering said shuttle; a brake disk rotatably supported on said outputshaft; a first pawl member arranged on said second half pulley; a secondpawl member arranged on said brake disk for engagement with said firstpawl member; a brake member on said film loop sensor movable responsiveto variations in the size of the film loop whereby .[.an increase.]..Iadd.a decrease .Iaddend.in film loop size causes said brake member toengage said brake disk to increase the rate of operation of said shuttlerelative to the rate of rotation of said capstan, and .[.decrease.]..Iadd.an increase .Iaddend.of said film loop size causes said brakemember to release said brake disk to decrease the rate of operation ofsaid shuttle relative to the rate of rotation of said capstan.
 2. Ashuttle speed control device as recited in claim 1 wherein said pawlscause axial movement of one of said half pulleys when said brake memberis engaged and removed from said brake disc responsive to actuation ofsaid loop sensor.
 3. A shuttle speed control device as recited in claim2 wherein said half pulleys cause said shuttle to be driven at differentrates responsive to the axial displacement of said pulleys.